Asynchronous transfer mode (ATM) is a flexible and efficient communication method, which is suited, inter alia, for realizing a wide-band ISDN. The information is transmitted in cells which typically have a constant and relatively modest length (53bytes). These cells are comprised of a header of 5 bytes containing, inter alia, address information, and of a part for transmitting information. They are transported and switched in networks having very high data transfer rates of, for example, 155 or 622Mbit/s. In addition to cells containing information, operation and maintenance (OAM) cells are included in the cell stream.
A typical feature of ATM switching is the temporary storing of the cells to be switched in FIFO (First In First Out) queues at the switches. This temporary storing causes variable delays, called switching delays, which occur in addition to the constant delays. The constant delays result from the line length at a given signal propagation rate across the transmitting medium (e.g., glass fiber) and from delays produced by signal processing processes used in transmission and switching technology.
The cell transit time, composed of the sum of all of the constant delays and of the sum of the switching delays occurring in all switching exchanges that are passed through, is an important parameter of service quality. It is, therefore, necessary to monitor switching delays in ATM telecommunication networks.